• Mating between single male and female is boring
  • species can reproduce without fertilization
  • individual of species can change sex
  • species can have both male and female sex organs
  • some populations have only a few that mate

• Two modes of reproduction in animal kingdom
  1. Sexual:
  2. Asexual:

• Animals exhibit cycles of reproductive activity

• Mammalian reproduction is governed by hormones

• Budding:
  • found among invertebrates

• Fission:
  • about the same size
  • found among invertebrates

• Fragmentation:
  • accompanied by regeneration of lost body parts
  • sponges, worms, starfish

• Parthenogenesis:
  • found among invertebrates and vertebrates

• Sexual reproduction commonly between male and female
  • but finding a partner may be difficult

• Stationary/slow animals can be hermaphroditic
  • individual have male and female reproductive bits
  • Any 2 individuals can mate

• Sex reversal occurs in different animal phyla
  • oysters are males first, then turn to female when larger
  • the largest female in some coral fish turn to male

• Cycles controlled by hormones and environmental cues
  • occur with asexual or sexual modes
  • often related to seasons

• Ovulation: release of eggs at midpoint of female cycle
  • cycles are variable in length
  • sheep: cycle + pregnancy = birth in spring

• Daphnia: cycles between asexual and sexual
  • seasonally related to environment
  • asexual when environments are stable….

• Fertilization = Fusion of haploid gametes
  • external:
  • internal:

• Moist habitat always required for external fertilization
  • spawning: when many individuals release gametes at the same time and place

• Fertilization = Fusion of haploid gametes
  • external:
  • internal:

• Pheromones: chemicals used to influence physiology and behavior
  • function as mate attractants
  • volatiles can be detected over long distances
  • pheromone production in humans is controversial

• Internal fertilization produces fewer gametes
  • survival of embryos higher

• Internal associated with protection mechanisms
  • parental care of young
  • shells, amniotic eggs, marsupials

• Parental care not just in vertebrates..

• External fertilization produces more offspring with lower survival rates

• Animals usually have gonads that produce gametes
  • testes in males, ovary in females
  • often established early in embryo development

• Many animals also have accessory organs
  • structures to carry, store, protect and nourish gametes
  • e.g. fruit fly (spermathecae stores sperm in female)

• Mating may occur with more than 1 male
  • males have mechanisms to prevent other male success

• Hormones coordinated across many glands/organs
  • hypothalamus, pituitary and gonads
  • endocrine system chemical messaging

• Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus (a region of the brain)
  • directs release of FSH (follicle-stimulating hormone)
  • directs release of LH (luteinizing hormone)
  • both from pituitary gland

• FSH and LH act on male and female gonads
  • stimulate reproductive hormone production

• Gonads then produce and secrete 3 hormones
  • testosterone, estrogen and progesterone
  • found in male/females in different amounts

• Embryos: develop reproductive structures

• Maturing mammals: induce sex characteristics
  • physical/behavior differences (male/female)
  • ‘Puberty’

• Mature mammals: play role in gamete formation and reproductive cycles

• Some females have linked menstrual cycle
  • 10 primates, elephant shrew, some bats, spiny mouse

• Ovarian cycle: series of changes in ovaries for maturation and release of eggs

• Menstrual cycle: prepares uterus for pregnancy
  • endometrium thickens with blood vessels
  • preparation for embryo implantation
  • if embryo does not implant, endometrium is shed

• Both cycles occur concurrently using same series of hormones